Welding of a vehicle body or the like, particularly, welding of a plurality of overlapped vehicle body plates (workpieces) is performed by an arc welding device. The arc welding device generates an arc and performs penetration welding of the plurality of workpieces by the arc.
An arc welding device disclosed in Patent Document 1 includes a plasma torch and a MIG (metal inert gas) torch. The plasma torch ejects plasma gas toward a plurality of overlapped workpieces to generate a plasma arc between the plasma torch and the workpieces. A wire-like filler is molten to fill from the MIG torch to the holes which are formed in the workpieces by the plasma arc, thereby welding the plurality of workpieces.
Furthermore, in Patent Document 1, the through holes formed in the plurality of workpieces are detected, and the flow rate of plasma gas is reduced after detection of the through holes. The arc voltages before and after reduction of the gas flow rate are measured, and the measurement result is compared with data obtained in advance. Thus, the lower hole diameter of the through holes is detected. When the lower hole diameter is detected, welding through the MIG torch is performed. When the lower hole diameter is not detected, welding through the MIG torch is not performed.